From after the conquest of the land by Joshua until the formation of the first Kingdom of Israel in c. 1050 BC, the Tribe of Gad was a part of a loose confederation of Israelite tribes. No central government existed, and in times of crisis the people were led by ad hoc leaders known as Judges. (see the Book of Judges) With the growth of the threat from Philistine incursions, the Israelite tribes decided to form a strong centralised monarchy to meet the challenge, and the Tribe of Gad joined the new kingdom with Saul as the first king. After the death of Saul, all the tribes other than Judah remained loyal to the House of Saul, but after the death of Ish-bosheth, Saul's son and successor to the throne of Israel, the Tribe of Gad joined the other northern Israelite tribes in making David, who was then the king of Judah, king of a re-united Kingdom of Israel. However, on the accession of Rehoboam, David's grandson, in c. 930 BC the northern tribes split from the House of David to reform a Kingdom of Israel as the Northern Kingdom. Gad was a member of the kingdom until the kingdom was conquered by Assyria in c. 723 BC and the population deported.

From that time then, the Tribe of Gad has been counted as one of the Ten Lost Tribes of Israel.

"The border was Jazer, and all the cities of Gilead, and half the land of the children of Ammon, unto Aroer that is before Rabbah; and from Heshbon unto Ramath-mizpeh, and Betonim; and from Mahanaim unto the border of Lidbir and in the valley, Beth-haram, and Beth-nimrah, and Succoth, and Zaphon, the rest of the kingdom of Sihon king of Heshbon, the Jordan being the border thereof, unto the uttermost part of the sea of Chinnereth beyond the Jordan eastward."

The location was never secure from invasion and attacks, since to the south it was exposed to the Moabites, and like the other tribes east of the Jordan was exposed on the north and east to Aram-Damascus and later the Assyrians.

According to the Torah, the tribe consisted of descendants of Gad the seventh son of Jacob, from whom it took its name. However, some Biblical scholars view this also as a postdiction, an eponymousmetaphor providing an aetiology of the connectedness of the tribe to others in the Israelite confederation.[3] In the Biblical account, Gad is one of the two descendants of Zilpah, a handmaid of Jacob, the other descendant being Asher; scholars see this as indicating that the authors saw Gad and Asher as being not of entirely Israelite origin (hence descendants of handmaids rather than of full wives).[4] In common with Asher is the possibility that the tribal name derives from a deity worshipped by the tribe, Gad being thought by scholars to be likely to have taken its name from Gad, the semitic god of fortune;[4] the name of Gad does not appear in the Song of Deborah, which scholars regard as one of the oldest parts of the Bible, pre-dating most of the Torah.[3]

Like Asher, Gad's geographic details are diverse and divergent,[4] with cities sometimes indicated as being part of Gad, and sometimes as part of other tribes,[5] and with inconsistent boundaries,[4][6] with Gilead sometimes including Gad[7] and sometimes not.[8] Furthermore, the Moabite Stone seemingly differentiates between the kingdom of Israel and the tribe of Gad, presenting Gad as predating Israel in the lands east of the Jordan,.[4] These details seems to indicate that Gad was originally a northwards-migrating nomadic tribe, at a time when the other tribes were quite settled in Canaan.[9]

In the biblical account, Gad's presence on the east of the Jordan is explained as a matter of the tribe desiring the land as soon as they saw it, before they had even crossed the Jordan under Joshua, and conquered Canaan. Classical rabbinical literature regards this selection of the other side by Gad as something for which they should be blamed, remarking that, as mentioned in Ecclesiastes, the full stomach of the rich denies them sleep.[4][10]